Allegations of incompetence and corruption around a botched green energy scheme in Northern Ireland have left many taxpayers questioning whether hundreds of millions of pounds of public money went up in smoke, a public inquiry has been told.

Allegations of incompetence and corruption around a botched green energy scheme in Northern Ireland have left many taxpayers questioning whether hundreds of millions of pounds of public money went up in smoke, a public inquiry has been told.

The furore over the renewable heat incentive (RHI) affair reached such a "fever pitch" that it struck at the very heart of the region's democratic institutions, triggering the collapse of powersharing at Stormont, a lawyer for the inquiry said.

Delivering his opening statement on the first day of the high profile independent probe, David Scoffield QC said "explosive" claims of political interference and improper patronage would be examined in forensic detail.

The inquiry will investigate the design and operation of the ill-fated RHI scheme, an eco-friendly state subsidy initiative that left the Stormont administration facing a potential £700 million overspend bill.

"It is hard to find a taxpayer in Northern Ireland who does not have questions to ask about how a scheme intended to do so much good turned out to have an unplanned bill of such proportions as to threaten other public spending priorities, apparently well into the future," Mr Scoffield said.

The RHI was established to incentivise businesses to shift to renewable energy sources by offering a proportion of the costs to run eco-friendly boilers.

But in Northern Ireland the subsidy tariffs were set too high and without a cap, so it ended up paying out significantly more than the price of fuel.

This effectively enabled some applicants to "burn to earn", getting free heat and making a profit as they did so.

Along with claims of incompetent handling of the scheme there have been more damning corruption allegations that steps to clamp down on the costs were subject to inappropriate political obstruction, with the intent of enabling others to benefit from the generous terms.

Democratic Unionist Party (DUP) leader Arlene Foster's role in the RHI scheme was at the heart of the row that brought down the Sinn Fein/DUP coalition government in Belfast.

She had a central role in establishing the RHI during her time as Stormont economy minister.

The DUP leader and former first minister, who will not be called to give evidence to the inquiry until next year, has insisted she acted correctly throughout.

A series of DUP party advisers, who have all rejected allegations of wrongdoing, will also appear before the probe chaired by retired judge Sir Patrick Coghlin.

Sir Patrick told the opening hearing at Parliament Buildings, Stormont, that the inquiry team has already examined one million pieces of documentary evidence.

"This inquiry was established in the wake of a media and political turmoil during which strongly worded allegations and repudiations were exchanged," he said.

"The inquiry was set up to provide a measured, objective, independent and publicly transparent investigation of the facts in accordance with the terms of the reference and that is what this inquiry shall seek to do."

Mrs Foster's refusal to accede to Sinn Fein's demand that she step aside as first minister pending the outcome of an inquiry prompted the late Martin McGuinness to resign as Sinn Fein deputy first minister in January, forcing the collapse of powersharing.

In the wake of the RHI furore, Sinn Fein repeatedly stated its unwillingness to return to devolved coalition government at Stormont with Mrs Foster as first minister until her actions were examined by the inquiry.

That demand has somewhat faded into the background as the powersharing impasse has been overtaken by a row over the Irish language.

Mr Scoffield noted there was "precious little" in the scope of the inquiry that was "uncontentious".

He said the inquiry would not deliberate on whether Mr McGuinness's resignation was justified.

But the barrister added: "It is undoubtedly part of the RHI story, that concern about what happened with this scheme reached such fever pitch that it struck at the very heart of our democratic institutions."

The said the RHI scheme had caught the public imagination in part due to allegations of "incompetence, corruption and improper patronage".

Mr Scoffield added: "The notion that money might be going up in smoke which could otherwise pay for doctors, nurses, teachers, policemen and so on has been anathema to many in the public."

The barrister made clear it was not the inquiry's function to determine civil or criminality liability.

He said the probe would also not be assessing whether all the individual RHI applicants were using it legitimately.

Mr Scoffield also referred to the explosive TV interview last December with former DUP economy minister Jonathan Bell who broke cover to level a series of allegations against Mrs Foster and DUP party advisers.

The lawyer said it was "probably unprecedented" in contemporary Northern Ireland politics for a former minister to turn on party colleagues in such a way.

He revealed the inquiry has secured texts and emails that were exchanged among politicians and officials in the wake of Mr Bell's interview.

Mr Scoffield said the inquiry was not concerned with the "political drama and theatre" of the episode but with the claims made by Mr Bell.

The RHI scheme was closed to new applicants when the scale of the overspend bill emerged, however Mr Bell alleged DUP advisers delayed this action.

After the eventual closure, Stormont ministers then took action to cut the tariffs they had pledged to pay in long-term contracts, a move currently being challenged by RHI boiler owners in the courts.

Mr Scoffield said many had been left "aggrieved" by the scheme, noting there were those in the renewables sector who felt the government "broke faith".

The inquiry will also focus on how whistleblower claims on the RHI were handled.

The opening session heard that one key whistleblower's application for anonymity had been declined by Sir Patrick.

Mr Scoffield confirmed that Mrs Foster and Mr Bell would not be called to give evidence until the "very end" of the inquiry's hearings.

This is expected to be well into 2018.

The barrister noted there would be those who would like to see the appearance of certain witnesses "fast forwarded" to an earlier date.

He said the sequencing of witnesses was a matter for the inquiry and would be determined solely on what was most conducive to its work, not on "other considerations".

Mr Scoffield's statement is scheduled to last three days.

After his opening remarks, the lawyer spent the remainder of the first day outlining in detail the chronology of events around the creation of the scheme.